Typical parallel manipulation systems are comprised of a stationary lower base plate and an upper movable platform. The platform is utilized to mount a workpiece or an instrument that is attached to the base by a plurality of strut assemblies that are positionally controlled by means of motor-driven linear actuators which, in turn, are controlled by an electronics circuit.
If the system utilizes six struts it is referred to as a hexapod. The hexapod allows the upper movable platform to be displaced within six degrees of freedom relative to the stationary lower base plate. The six degrees of freedom include three translational movements and three rotational movements.
Prior art hexapods typically utilize actuators that are operated by servo motors, stepper motors, linear piezoelectric motors, and inch-worm type motors. The stepper motors in conjunction with a ball or lead screw can produce a backlash that adversely affects the selected length of the struts, linear piezoelectric motors can produce a vibration that can affect the positioning of the struts, and the inch-worm type motors can produce hysteresis that can affect the accuracy and repeatability of the hexapod.
The parallel kinematic positioning system disclosed in the instant application eliminates or at least minimizes the above listed problems by utilizing an ironless-core, linear-shaft servo motor that operates in combination with a magnetic load counterbalance.
A search of the prior art did not disclose any literature or patents that read directly on the claims of the instant invention. However, the following U.S. patents are considered related:
U.S. Pat. No.INVENTORISSUED6,769,194Hennessey 6 Jan. 20046,474,915Wildenberg 5 Nov. 20025,279,176Tahmasebi et al18 Jan. 19944,819,496Shelef11 Apr. 1989
The U.S. Pat. No. 6,769,194 discloses a method and an apparatus for providing nanometer precision motion. The apparatus includes a parallel kinematic micromanipulator that is formed using at least three or six kinematic links. The kinematic links include a high resolution, non-contact encoder that provides position information. Movement of the micromanipulator is effected using piezoelectric linear actuators that connect with each of the kinematic links. The combination of the parallel kinematic structure and the piezoelectric linear actuators provide three or six degrees of freedom.
The U.S. Pat. No. 6,474,915 discloses a hexapod that is used to position a tool with respect to a part that is to be machined. The hexapod includes two spaced plates that are interconnected by six articulated and extensible legs. The two plates, including a base plate and a mobile plate and the six legs, are joined for varying the relative position of the mobile plate with respect to the base plate. The hexapod further includes a device for reducing stress on the elements that comprise the hexapod.
The U.S. Pat. No. 5,279,176 discloses a six-degree of freedom parallel-manipulator having three inextensible limbs that are attached to and manipulate a platform via universal joints. Each of the inextensible limbs are attached via universal joints to a two-degree of freedom parallel driver such as a five-bar lineage, a pantograph, or a bidirectional linear stepper motor. The drivers move the lower ends of the limbs parallel to a fixed base and thereby manipulate the platform.
The U.S. Pat. No. 4,819,496 discloses a six degree of freedom micromanipulator assembly that is interposed between the fingers and the arms of a robotics structure. The accuracy of the assembly depends upon the position of the fingers relative to the arms of the assembly.
For background purposes and as indicative of the art to which the invention relates, reference may be made to the following remaining patents found in the search:
U.S. Pat. No.INVENTORISSUED7,270,319Culpepper18 Sep. 20077,148,646Matsushita12 Dec. 20067,081,866Gaechter25 Jul. 20066,671,975Hennessey 6 Jan. 20046,648,583Roy et al18 Nov. 20036,497,548Roy et al24 Dec. 20026,236,451Wildenberg22 May 20016,021,579Schimmels et al 8 Feb. 20005,870,834Sheldon16 Feb. 19995,836,083Sangwan17 Nov. 19985,797,191Ziegert25 Aug. 19985,333,514Toyama et al 2 Aug. 19945,028,180Sheldon et al 2 Jul. 19914,988,244Sheldon et al29 Jan. 19914,790,718Vickers13 Dec. 19884,655,549Jue 7 Apr. 1987